I had the pleasure of experiencing genuine hypothermia symptoms: I thought there was something wrong with the bike as my legs started slapping the tank. No, that was uncontrollable shivering. Mind started getting really fuzzy, couldn't concentrate or focus properly on what I was doing. Wasn't even that cold. 25 when I left Vegas, but it climbed steadily to maybe 50, but by that time I was already chilled to the bone. Stopped every 40 miles and that helped, you immediately get warm once you remove he 70mph windchill. Could not have worn any more layers than I already did. Heated vest is on the wish list.
And yes, it's equally bad in summer at 115 degrees. Likely I will have to make the trip fairly regularly, ugh. A good reason to get my airplane project finished and flying; that's a pleasant way to do an otherwise seriously dull trip. There really is no scenic route to go unless you want to double the mileage.